1. Field of the Invention
The present invention relates to a wheel-state obtaining apparatus including wheel-side devices and a body-side device that are provided on a vehicle, and a method of obtaining wheel-position information, with such a wheel-state obtaining apparatus.
2. Discussion of Related Art
Examples of such a wheel-state obtaining apparatus are disclosed in JP-3212311B2, JP-2003-175711A and JP-11-20428A. The wheel-state obtaining apparatus disclosed in JP-3212311B2 is arranged such that when an operator of the apparatus enters, into an information processing device of the body-side device, wheel-position information representative of a position of a wheel a tire air pressure of which is to be adjusted, the wheel-side device corresponding to the wheel in question transmits wheel-side information including identification data and air-pressure data, in response to a change in the tire air pressure, and the information processing device stores the identification data and the wheel-position data in relation to each other, when the wheel-side information is received by the information processing device.
The wheel-state obtaining apparatus disclosed in JP-2003-175711A is arranged such that an electric wave transmitted from each of a plurality of wheel-side devices provided for respective wheels of a vehicle is received by a receiver antenna of a body-side device of the vehicle, the body-side device determines the position of the wheel corresponding to the wheel-side device from which the electric wave has been received. The body-side device determines the position of the wheel in question, on the basis of a pattern of periodic change of a voltage of the received electric wave during rotation of the wheel, and stored patterns of periodic change of the voltage of the electric waves transmitted from the respective wheel-side devices.
The wheel-state obtaining apparatus disclosed in JP-11-20428A is arranged to estimate a tire air pressure of a wheel under examination, on the basis of the tire air pressure of a reference wheel, and a ratio of a dynamic load radius of the wheel under examination to that of the reference wheel, and to determine the position of the reference wheel relative to the vehicle body, after a position change of the wheels, on the basis of a state of change of acceleration value of each of the front right and left wheels and rear right and left wheels when teach wheel runs over a raised portion of a roadway surface.